The invention relates to an acoustic element and method for sound processing. The acoustic element (1) is made of a porous stator plate (2) which is either electrically conductive or plated on at least one of its surfaces to be conductive. A moving diaphragm (3, 3a, 3b) has been attached to the stator plate (2). To measure as well as produce sound pressure and particle velocity, the equipment comprises two pairs of aforementioned acoustic elements (1). elements serving as sensors control elements serving as actuators to attenuate and absorb sound.
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1. An acoustic element having a plate-like structure, comprising
first and second porous stator plates which are either electrically conductive or plated on at least one side to be electrically conductive, and at least one moving diaphragm with at least one electrically conductive surface, and said diaphragm being arranged for movement in relation to said stator plate, wherein said first and second stator plates are arranged symmetrically to opposite sides of said diaphragm and said diaphragm being arranged for movement toward and away from each of said first and second stator plates; and wherein each of said stator plates includes a facing surface facing said diaphragm with the facing surface of each stator plate being formed such that air gaps are formed between the diaphragm and the stator plates and wherein said diaphragm is arranged to move symmetrically relative to said first and second stator plates. 13. A method for sound processing, in which at least one property of a sound field is measured, and on the basis of the measurement result an attenuation sound is produced by at least one actuator,
wherein the method for sound processing involves at least two dipole sensors and at least two dipole actuators, said sensors and actuators comprising at least one porous stator plate which is either electrically conductive or plated on at least one of its sides to be electrically conductive and of at least one moving diaphragm with at least one electrically conductive surface, wherein said stator plate and diaphragm constitute a stacked structure in which the sensor signals are coupled to control the moving of the dipole actuators for adjusting the sound pressure and the particle velocity to match the desired value signals, said method further comprising forming a product of the particle velocity signal and the impedance control coefficient Z1, subtracting the sound pressure signal from said product to provide a difference value, amplifying the difference value by a gain coefficient (G2), and inputting this signal to control the movements of the actuators.
11. A method for sound processing, in which at least one property of a sound field is measured, and on the basis of the measurement result an attenuation sound is produced by at least one actuator,
wherein the method for sound processing involves at least two dipole sensors and at least two dipole actuators, said sensors and actuators comprising at least one porous stator plate which is either electrically conductive or plated on at least one of its sides to be electrically conductive and of at least one moving diaphragm with at least one electrically conductive surface, wherein said stator plate and said diaphragm constitute a stacked structure in which the sensor signals are coupled to control the moving of the dipole actuators for adjusting the sound pressure and the particle velocity to match the desired value signals, first, second, third and fourth electrodes are provided as sound pressure or particle velocity actuators and wherein the first electrode serving as one of said sensors controls the second electrode serving as one of said actuators, multiplied by a coefficient -p, and the third electrode serving as one of said sensors controls the fourth electrode serving as one of said actuators, multiplied by a coefficient p.
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5. An acoustic element device comprising two or more of said acoustic element of
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15. A method as recited in
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The present invention relates to an acoustic element having a plate-like structure.
The method further relates to a method for sound processing, in which at least at least one property of a sound field is measured, and on the basis of the measurement result an attenuation sound is produced by at least one actuator.
In order to determine acoustic variables, both the sound pressure and the particle velocity must be known. These may also be used to determine acoustic impedance, which is the quotient of the sound pressure and the particle velocity. To control acoustic properties by active control methods and equipments, it must be possible to measure and adjust the aforementioned variables.
It is known to employ an electrostatic loudspeaker made of perforated plate for producing sound. The loudspeaker has a plate-like structure, but its drawbacks include a strong resonating tendency of the plate structure. In addition, electric shielding of the structure is problematic.
It is the object of the present invention to provide a simple and efficient acoustic element and method for sound processing.
The acoustic element according to the invention is characterized by comprising at least one porous stator plate which is either electrically conductive or plated on at least one side to be electrically conductive, and at least one moving diaphragm with at least one electrically conductive surface.
The method according to the invention is further characterized in that at least two dipole sensors and at least two dipole actuators, said sensors and actuators consisting of at least one porous stator plate which is either electrically conductive or plated on at least one of its sides to be electrically conductive and of at least one moving diaphragm with at least one electrically conductive surface, constitute a sandwich structure in which the sensor signals are coupled to control the moving of the dipole actuators for adjusting the sound pressure and the particle velocity to match the desired value signals.
The basic idea of the invention is that the acoustic element consists of at least one porous stator plate which is electrically conductive or plated on at least one of its surfaces to be electrically conductive, and of at least one dielectric moving diaphragm with at least one electrically conductive surface. The idea of another embodiment is that the element consists of at least two porous stator plates and a moving dielectric diaphragm between them. The idea of yet another embodiment is that the moving diaphragm is permanently charged as an electret diaphragm. Further, the idea is that the elements according to the invention constitute a sandwich structure so that it has at least two dipole sensors and at least two dipole actuators, the sensor signals being coupled to control the moving of the actuators for adjusting the sound pressure and the particle velocity to match the desired value signals.
The invention provides the advantages that the element has a simple structure, problems resulting from resonating are non-existent, and its electric shielding is easy. Further, the sandwich structure contributes to efficient production, measurement and attenuation of sound.
The invention will be described in more detail in the accompanying drawings, in which
An advantageous embodiment of the invention is represented by one where the measured signal of the electrode A is coupled, amplified with coefficient -P, to the movement-producing element D, and the movement signal measured from the electrodes B is coupled, amplified with coefficient P, to the electrode C, as illustrated by FIG. 5. This produces a control corresponding both to the sound pressure and the particle velocity for producing a reverse sound field and for preventing the sound field from propagating through the element in noise attenuation embodiments.
It is typical of all the above equipments illustrated in the Figures is that the sum of two signals e.g. A+B correspond to the sound pressure and the difference A-B corresponds to particle velocity. Similarly, by controlling the elements C and D in a cophasal manner it is possible to implement a monopole actuator producing sound pressure, and by controlling the elements C and D in a differential phase it is possible to implement a dipole actuator producing particle velocity. The aforementioned principle is applicable in many ways to sound reproduction equipments, active sound controlling, acoustic correction, and to embodiments of active noise attenuation.
A most advantageous control method is shown by
The drawings and the description related thereto are only intended to illustrate the idea of the invention. The invention may vary in details within the scope of the claims. As the modules also contain components that absorb sound passively, the modules may be used for attenuating and absorbing sound in the entire sound spectrum, although the active, electronically implemented portion in the system works best within the frequency range 0-1 kHz. Hence, it is worth while to filter frequencies higher than this off the control system. The simplest implementation of the invention may be an element having a porous metallized plate in the inner surface, with a moving diaphragm arranged in the surface of the plate. Such a sound element may also be rolled up. It should be noted that porous stator plates as such attenuate high frequencies and prevent harmful acoustic reflections. Several attenuating elements according the invention may be placed on top of each other to add to the efficiency. A wall structure with two elements positioned facing each other as a mirror image is most advantageous.
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